Intercommunicating system



Feb. 19, 1929.

E. W. NILES ET AL INTERGOMMUNICATING SYSTEM 'Filed Feb. 25, 1928 N E M W W w INVENTORS Z. wwzeswnrzzzwvw ATTORN EY Patented Feb. 19, 1929.

UNITED STATES PATENT OFFICE.

ELIOT W. NILES, OF BLOOMFIELD, NEW JERSEY, AND WILLIAM H. EDWARDS, OF FLUSHING, NEW YORK, ASSIGNORS TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

INTERCOMMUNIOATIN G SYSTEM.

Application filed February 25, 1928.

Th invention relates to improvcmentsin intercommunicating systems, and more parcularly to improvements in the ringing or sling arrai'igement-s associated therewith. In an intercoinmunicating system having a plurality of stations connected thereto, it is generally necessary to provide arrangemeats for preventing ringing current, trans mitted when one station signals another station, from traversing stray paths and causing false operation of the signaling means at other stations. One of the methods for pro-- venting such false operation has been to connect a conducting strap between the positive side of the ringing battery and thenegative side of the central office battery and thus provide a means of shunting stray current paths which would otherwise tend to ring all other stations having their signaling circuits closed. It has been found that while such a strap connection might short-circuit these stray ringing paths, nevertheless it mtroduced an undesirable heavy drain onthe ringing battery. In the arrangements of the pres entinvention, the conducting strap is not utilized... Rectifiers, referably of the con tact type, are insertec in one side of each of the talking current supply circuits leading to each ofthe pairs of lines used for intercommuuicatiom These rectifiers are poled so that the flow of talking current to the pairs of inter-communicating conductors is not hindered, but current in the opposite direction, due to the stray ringing paths, is largely reduced. Among the advantages of the arrangements of the invention over former systems, is large reduction in the maintenance of the rin' ing battery dry cells by reducing their drain to appr .nnately one-third of its previous va ue. A further advantage conin the fact that for outside central ofiice connections the arrangements oi the invention permit using three-wire trunks with only one induction coil and. condenser per trunk instead of providing this equipment at each station. Such arrangements have previously been consirhired unsatisfactory, due to the click produced by the excessive current required for ringing. A further advantage that the signaling means at each station may consist of regular direct current apparatus instead of polarized apparatus. Fun flier too turns and objects of the invention will Serial No. 257,010.

appear more fully from the detaileddescrip tion hereinafter given. The invention may be more fully understood from the following description, together with the accompanying drawing, in which is shown a circuit diagram embodying a prelerred form of the invention. I

In the drawing is shown an intercomrnunicating system having three pairs of intercomniunicating conductors L L and L Three separate stations are shown, such as 1, 2, and Each station would be provided with a set of switching means, such as the keys K K and K for intercommunicating between each other. Each station would include signaling means, such as the buzzer arrangements 12, 13, and 14. n A source 11 ofringing battery is provided for thesignalin arrangements. To provide current'for ta king purposes, a talking battery 4 is shown. This is connected to the lines L L andL through conductors including the retardation coils 5. 6, 7, 8, 9, and 10. In the negative leads from the talking battery to the pairs of intercommunicating conductors, are inserted the rec tifiers 26, 27, and 28. These rectifiers may be of the contact variety and are so poled that they will readily transmit the current from the battery 4 to the lines.

The invention may be more fully understood from the following description of its operation. If the subscriber at station 1 desires to communicate with the subscriber atstation 2, the key K atfstation 1 will be operated to its extreme position to make contact with bus-bar 20. This willclose the following signal path: from the negative terminal of ringing battery 11, conductor 18, bus-bar 20, lower outer contact of key K ring conductor of line L,, conductor 24, signal apparatus 13, conductor 19, to the positive side of the ringing battery 11. This will operate the signaling device 13. In order to more fully understand the arrangements 01. the prior art, let it be assumed that the rectifiers 26, 27, and 28 are not included in the circuit arrangements. Accordingly, it will be seen that the ringing current will also traverse the following stray path: from the ring conductor of line L,,, through the path including retardation coil 8, thence through the path includin retardation coil 10, over ring conductor of line L, thence over conductor 25, si naling apparatus 14, conductor 19, to the positive terminal of ringing battery 11. The ringing current traversing this stray path would tend to operate the signaling means 14. Obviously, this would not be desired, as station 1 desired to exclusively signal station 2. One of the methods of preventing such false signaling, which has been utilized in the past, has been to connect a conducting strap, such as 17, between the points 15 and 16, or, in other words, between the positive terminal of the ringing battery and the negative lead to the talking battery. With the strap 17 connected as desired, the ringing current which traverses the stray path, including retardation coil 8, would be shunted across the strap 17 to the ringing battery and would not affect the signaling means 14. However, as has been pointed out, it has been found that this strap connection 17 introduces an undesirable heavy drain on the ringing battery. Accordingly, in the arrangements of the invention the strap 17 is omitted and the rec tifiers 26, 27, and 28 are included in the con ductors from the negative terminal of bat tery- 4 to the conductors of lines L L and L Accordingly, when station 1 signals station 2, there will be a path for stray currents over the ring conductor of line L through the rectifier 27, retardation coil 8, retardation coil 10, rectifier 28, to the ring conductor of line L to the signaling means 141 and thence to the ringing battery 11. However, this path will be very high in resistance due to the polarity of the rectifier 27 and sufficient current to affect the signaling means 14 can not flow thereover. In a similar manner, stray ringing currents will be prevented from flowing to other stations by the polarity of" the other rectifier arrangements, thus preventing false signaling operation.

It is pointed out that while only three lines, such as L L and L and three stations are shown, nevertheless arrangements of the invention are applicable to an intercommunieating system having a different number of lines and stations. Accordingly, while the arrangements of the invention have been disclosed as embodied in certain specific arrangements which are deemed desirable, it is pointed out that they are capable of embodiment in other forms without departing from the spirit of the invention as defined in the appended claims.

What is claimed is:

1. An intercommunioating system comprising a plurality of pairs of lines, a plurality of subscribers sets, signaling means individual to each subscribers set, means to connect said subscribers sets and signaling means to said pairs of lines, a source of talking current for said lilies, and rectifiers in the conductors connecting one side of said talking source to said lines.

2. An intercommunicating system comprising a plurality of pairs of lines, a plurality of subscribers sets connected to said lines signaling means individual to each sub scribers set, a source of signaling current, means for completing signaling circuits from said source to said signaling means over one of the conductors of each of said pairs of lines, a source of talking current having one side connected to said last mentioned con ductors and rectifiers in the leads between said talking battery and said last mentioned conductors.

3. An intercommunicating system comprising a plurality of pairs of lines, a plurality of subscribers sets connected to said lines, signaling means individual to each subscribers set, a signaling source, means for completing signaling circuits from one pole 01? said source to said signaling means over one of the conductors of each of said pairs of lines, a source of talking current for said lines having one pole connected to said last mentioned conductors, and rectifiers in the leads between said talking source and said conductors, said rectifiers being poled so as to allow transmission therethrough of current from said talking source and to oppose the transmission therethrough of current from said signaling source.

In testimony whereof, we have signed our names to this specification this 24th day of February, 1928.

ELIOT W. NILES. WILLIAM H. EDWVARDS. 

